tanner



Feb. 5, 1929.

H. L. TANNER GYROSCOPIC com/ass Filed May 13, 1921 6 Sheets-Sheet 1INVENTOR .Feb. 5, 1929.

H. L. TANNER GYROS COPIC COMPASS Filed May 13. 1921 6 Sheets-Sheet 2INVENTOR flarlyljanmr ATTORNEY/5.

Feb. 5, 1929. I 1,701,283 H. L. TANNER GYROSCOPIC COMPASS Filed May 13'.1921' 6 sheets-sheet 4,

i INVENTO/ 10 g HaWyLTalmer A TTORNE 2*,5'

Feb. 5, 1929.

H. L. TANNER GYROSCOPIG commss' Filed May 13; 1921 s Sheets-Shed 5 INVENTOR Harr yl. farmer B Y Mm M7 1 if:

A TTORNE g5 reiterated Feb, 5%,

f: the

HARRY L. TANNER, OF BROOKLYN, NEW YORK, ASSIGNOR TO FORD INSTRUMENT COM-ranr, run, or NEW YORK, n. *1,

A CQRPGR-ATION OF NEW YORK.

GYBGSCOFLC COMPASS.

Application filed lvlay 13,

This invention relates to meridian seeking gvroscopic compasses.

i i ie eari exaernnenis l Follouin tl 1 1 of on cault with'a gyroscopiccompass in which meridian seeking properties were imparted to agyroscope by suppressing one of its three degrees of freedom, manyattempts have been made to overcome the disadvantages of the early typesof compass and produce instruments better adapted for use on ship boardthan were the early experimental devices. A number of instruments havebeen proposed, some of which have gone into use, but all of them, so faras I am aware have been constructed along the general lines of theoriginal Foucault compassflay arranging the gyroscopic element to havethree degrees or" freedom, one about its spinn ng axis and the othersabout two supporting axes perpendicular to each other and to thespinning axis, one of the supporting axes being vertical and the otherhorizontal. In order to cause the gyroscopic element to seek themeridian one of its degrees of freedom usually that about its horizontalsupporting axis, is suppressed, as by making the element pendulous or insome other suitable manner.

An instrument of this general type is subjcct to ballistic deflectionsdue to acceleration and retardation pressures and to the e'l'l'ect uponsensitiie element of oscillatorv motion of the craft upon which it iscarried. ltis also subject to deviations due to meridional components ofthe movement of the craft, this deviation being affected by course,speed and latitude.

The development of the Foucault typeof compass has been concernedchiefly with the improvement of structural features and the provision ofarrangements for correct- I r the errors due to the causes menabovet inorder to render the instruments suitable tor navigation purposes. but inall the plane of rrwtion of the a'vroscoj has been kept per uuulicularto the surface of the earth, and its spinning axis parallel thereto.

in types of compass at present in use the sensitive element suspendedfrom a follow-up or phantom element by means of a filament or is carriedupon a mercury float arrangement or supported upon a film of oil or thelike. These arrangements are open to many objections, require frequentand lu u 1921. Serial No. 469,201.

careful adjustment, and renewal. of liquids in case t io latter areused, and increase the cost of the complete instrument.

The'follow-up element upon which the sensitive element may be mounted inany of the ways mentioned above carries the compass card and is arrangedto be moved in azimuth by means of a motor controlled by a deviceconsisting of a contact member associated with the sensitive element andmovable in azimuth therewith about the vertical supporting axis. Thiscontact member cooperates with a pair of contact members associated withthe follow-up element, the arrangement being such that upon relativemovement in azimuth between the gyroscope and the craft due to a changein course, the movable contact member will engage one or the other ofthe contact members of the pair to energize the motor and cause thefollowup element to move with the gyroscope and tl erefore be displacedwith respect to the lubbers line to indicate the new course, the lubbersline being placed upon a part of the instrument which is fixed withrespect to the craft, except as it may be movable to correct for thedeviations due to meridional components of the movement of the craftunder varying conditions of speed and Course.

Various methods have been employed for correcting for such deviations,to which all gyroscopic compasses at present in use are subject. Thereadings of the compasses may be corrected mathematically by means ofdata obtained from suitable correction tables or mechanically, by meansof mechanism movable in proportion to the correction which should beapplied. The arrangement commonly employed for this purpose is one inwhich the lubbers line is mounted upon a movable member which is shiftedin accordance with the several factors which enter into the resultingcorrection, such as heading, speed and latitude of the craft.Arrangements of this kind arecomplicated require careful adjustment anddo not. take care of all. of the factors entering into the deviations.

To cause the sensitive element to seek the meridian means are providedfor applying a torque about its horizontal supporting axis to cause itto precess about its vertical supporting; axis toward the meridian. Thistorque is usually applied by the force of fit) gravity acting upon thegyroscope either directly, as by making it pendulous, or indirectly asby connecting thereto a pendulous mass or liquid level arrangement. inall of these arrangements the ettect upon the torque applying device oracceleration or retardation pressures due to changes in course or speedof the craft will result in ballistic deflections which must becorrected in order to obtain true, rezuliupjs under the new conditionso1" course or speed.

In instruments of the general types referred to above, failure of thefollow-up motor to tuuetion properlr may result in injury to theinstrument due to the procession caused by the torque applied about thevertical axis by turning of the craft.

It is an object of this invention to provide a gryroscopic compass whichshall possess, among others, the following ad vantages over prior typesof instruments.

The use of delicate mechanism for sup porting the gyroscopic element isavoided, therey sin'iplitying the construction of the instrument,lessening its cost and eliminating; the necessity for frequent andcareii d adjustments.

Displacement of the compass card element due to meridional components ofthe speed of the craft upon which the compass is carried is prevented,so that the element will occupy its true position with respect to thepoints of the compass, and the lubbers line may occupy a fixed relationto the craft instead of being movably mounted to permit it to be shiftedin accordance with the correction which should be applied as in priorcompasses.

The instrument so constructed that the degrees of freedom of itsgyroscopic ele ment about two mutually perpendicuh r supporting axes maybe suppressed in order to cruise the element to follow the movement ofthe craft over the surface. 01 the earth and maintain its normalrelation to this surt'ace iinlependently of latitude. By virtue of thisconstruction the eti'ect upon the element ot acceleration andretardation pi res due torchanges in speed oi? the emit will beautomatically taken care ot, and suvh corrections as may be necessary tomeet new conditions of speed, can be easily applied.

The arralurenient ot the parts oi the instrun'ient is onethat makes thebest use of the space available and results in an instrument of compactdesign in which the compass card entirely unobstructed thereby renderingthe instrument particularly adapted tor direct observations. The outerparts of the instrument which carry the compass card and the lubbersline need not be as accurately balanced as in other types. T his is ofparticular advantage when azimuth sighting devices are used with theinstrument, as their weight and the pressure exerted upon them duringuse will not produce a disturbance of accurately balanced parts, as isthe case with other forms of gyrpfhtoplc compasses.

ihe instrmnent is not liable to 1n ury due to failure of any of itsparts to tunction properly and may be easily restored to operativecondition when the detect has been remedied.

The above advantages of the invention, as well as others wh ch willhereinafter up} Hi1, are attained by providing a mass, such. as therotor of an electrically driven pyroseop which is arranged to spin aboutan axis having a substantially constant inclination to the surface ofthe earth and normallybearing a tixed relation to the plane of themeridian. The rotating mass is surrounded by a also which serves as asupport for the mass and may turn in the plane of the mass about theinclined axis of the latter inde pendently ot the rotary movement oitthe mass within the ease. The coils constituting the stator of thegyroscope may be mounted within the case.

The case is mounted within an inner supporting member upon an axislying; in the plane at the case. The inner supportii'ig member may bemounted upon a ln'irizonta axis perpeiulicular to the supporting axis ofthe case within another supporting member which in turn is mounted upona horizontal. axis within a horizontal inner frame, or the innersupporting member may in some cases be mounted directly upon the frameupon a horizontal axis perpendicular to the supporting axis of the case.

The use of vertical bearings which, even it of the ball type, are lesssensitive than are lmrizontal bearings, is thus avoided, and it ispossible to use knife edefc beari throughout. the instrument to lessentrict or for any o'tl er reason. No torsion suspensions, mercury floats,oil film hearings or other delicate supporting arrangements are necesary, and all oi the d' a"vantages lending their use are entirelyeliminated.

The inner :trame which may carry no compass card of the instrumentmovably mounted upon an outer frame which ha." a tixed relation to thecraft. upon which compass carried. as by being: mounted the gimbali'l'iljQjS of a biunacle, and may bear the lubbers line. 0;) a'ativelyconnected to the inner frame a driving element, such as an electric serotor controlled by contact mechanism c ing in general of two relativelymovable parts one of which is con nectcdto the case or to a part ot theinstru ment adapted to move with the case,

and r... other of which is connected to some other part of theinstrument, such as one of the supporting lfl'ltillll'lell, which bearsa fixec relation to the case when the latter occupies Cir ' great circlealong which the craft is passing iis normal position but which isdisplaced with respect in the ease when the iaii 'er meridian, rela vennweinent he tween he frames due to cnanges in course of ire i. tend toturn fhe e: ie about ;he rofor and displace the parts of the contactmechanism wii'h respeci 'iio each other. This Will cause thz, drivingmotor to turn the inner frame and (he case in a 'duecfion oppi site tothat in which these members will fend in be turned by fire movement ofthe craft. This r verse 1.; ,vemeiiii wiil continue until the parts ofthe e echanism are I brought hack (0 their norina liPiIlUZL fhcrcbystopping the actuation of the motor.

This sequence of operafions wili he repeated continualiy so long as thecourse of the craft is changing with the resrif that the driving motorWili always inain -ain the case and the inner frame in a definiterelation to the rotating mass While the outer frame Wiil move with thecraft relatively therefo. providing the inner fr: me with a compass cardand the oufer mine with a lubbers line, the inst-ruinene will give acontinuous indication of the course of rho craft.

On account of the inclined position of the gyroscopic element thedegrees of freedom about both of its supporaing may be suppressed bymaking the ele-I. entoenduious about the axes so that "the Toot upon theelement of changes in cour e or speed of the craft upon which shecompass is carri ed in a be automatically faken care of. 1 en the menswill cause ii to assume a certain nciinai'ion to the surface of theearth. As

fhe craft begins to more its accolera" cause a torque fo he about anaxis lying V piano perpendicuiar in he p" ,Ireai circle along): whichi'ho cra I rhich will *a-usc "(he chuucnl in pre 3- ahoui an axis afright angles 'iherei'o. i. 0., an axis lying: in ihe plane of theyuillilli and in ihc pl of ihe great circle. duh 'usiurz.v of iheelement will then produce a torque about the precession lXln' which will:ausc precession aboit the axis ahorfio which a torque was firstapplied. 1 y properly pr portioning the parts the element may be made toprecess about an axis lying in a plane per 'iendicular to the plane ofthe iis plane and in a at an angular Velocity equal to that o khe craftand in the same direction. The pyroscopic element Will thus foiiow themore of the craft as speed iin-:'case and the speed has become consi'auithe will assume such a posiiion as 10 ctuse the necessary precession tomaintain its inch'narion co- "taut as the craft travels over the surfacethe earth.

In order to prevent errors in the inch- 5 V of "ii-he insiruni due to'i'he ei'l'ect (i kiai. scopic eiein he nyz eat of (he more- 3 hecrafi'. the par: of the contact as sin which is carried upon one of thehe for supporfii ihe gyri'mcopic element is arranged to be shiftwl inaccorda: "cii'h die amount by which the part of she incchanisnl which isassociafel with the case would be shifted as rcsuit of ihe T-CQS i acaused by he pendulcusness of (he lenient explained above. The drivingmoi'or therefore pre ii'ed from being; energized and There is no displaI the compass card eiement f or :1

position. The mechanism for iihe contacts to produce compensation the lthe effect upon de gyroscopic (lclliiiliI c movement of the craft maybe" manual automatically operated in accordance with the factors uponwhich the cifeccs depend will nore clearly appear hereinafter.

Since the case is arran 'ed to turn freely aboutthe rotor there will heno danger of jury to the parts of the instrumeu if the iving motor failsto perform its function in keeping the inner frame and case in theirnormal position with respect to the rotor. As the crafiturns, fheseparfs will simply be carried around the rofor and may be easily restoredto normal posi ion when the motor has again heen started info operation.There is thus no danger o' instrument being injured, even if file )icroiior is not sfopped when (he ll'lOi'Ui 1 v. i" (ll Variousarrangcmenfs may be employ-X for lam the oscillations about the 1:10(han of the Q'YlfOSCOplC elcinenii of (he f- [11illl03i". ()ucarrangement for i'his purpose ((mSlSiS of a mass which affached 10 thecase in the manner of a pendulum osciilaigions.

iien't that may be emphyod cons of a pan: of liquid containingreservoirs ii oun' d i i i he iorih-soufh plane and connected by arestricted passage.

The particular nature of the invention as Well other ohjeci's andadi'aniag'es the eof appear more clearly from a descri' of the apparatusshown in the accompanying drawings in which 2 s simplified QlGVlLiflll,partly in section. of the instrument oi. ldig. l YlQWQd from the west,

Fig. 3 is a plan view but with certain pm on i p L fl arrangement -fordainpilz the oscillations ol the compass,

Fig. 4 is an elevation similar to that of Fig. 2, ol' the form ofinstrument shown in Fig. 3,

Figs. 5 and (3 are ,'ector liagrrmns relating to the dumpingai'rutugmueat shown in Figs. 3 and 4:,

Fig. 7 represents the paths traced out by the north-south axis ofuudsunped and damped ferns o'l compasses Fig. 8 is a plan view similarto Fig. l of a. preferred embodiment of: the invention with the hinhaclecase omitted.

Fig. 9 is an elevational 'icw ot the entire inr-itriunent principally insection along the line u9 of Fig. 8,

Fig. 10 is a plan. View, partly in see end with the main roscoperemoved,

11. is an elevation or the north re-t ortion of the compass as seen 1'3.1' 1e giinhel rings of the hinnacle,

Fig. 12 is an elevation oi? the south w t portion of the ii'istruinentnving the motor and the tra usniitter for LIC LULZt peater con'ipasses,

Fig. 13 is an elevr ion of a portion of the south side of the inlllll'llcilt showing the correcting mechanism,

Fig. 14; is a simplified diagram of the circuit connections or theinstrument.

Fig. 15 is a simplified p an o' element having another nient appliedthereto,

Fig. an elevation of the ole shown 1:. and

an cleratioral view of one of the truhnit s oi the gyroscope.

The general structure of the h print-i to of operation will first he l Jthe diau'r-ius. h

Referring particularly iustruumnt coin;

the r ses a g 1 of any suitehle (351.. auction. the which is mounted inuppe 22rd ings of a case 3 surrou; 1, provided with ventilationapertures dicated in Fig. 1. The case 3 is proridet with trunnions lmounted f heeriugs in an inner r' 5 which in is provided With trunnionst5. 6 mounted in hearings in a second ring 7 which. on account of it.)func- 1 is a plan View with ports (omitted tion, will he hereinafterreferred to as the stabilized ring of the ins rument. The gyrcscopic eleout and its supporting ring 5 mounted in an inclined position shown mostclearly in the elevational view Fig. by displ cine; the axis 6() fromthe center 7 y, C. G, of the element so that the element 's pendulousand maintains an inclination to the surface of the earth when the rotoris not spinning. This angle will h ell positions ol' the compass.

inning the inclination cinent will drier from its inclination ot the ewien ti rotor is at by an angle OLL which depends upon the latitude andan angle which depends noon the east-West component of the speed of thecraft upon which the compass is carried, as will hereinafter heexplained. The normal inclinetion of the elem rent with the rotorspinning may therefore he 1 noted by o o. ag.

'lhe stabilize:

trunnions 8 8 disposed at right angles to the trunnion {HUS (3-6 and inthe plane ot th trunnion axis 4-4. The truunions 8 8 are mounted inhearings in an inner irame or r11 9 adapted to power driven and hearinga- .scale gizduoted in units of angular measure. This frame is rotatablymounted hin an outer tt'rzrne or shell 10 by in ftztlS oi halls ll. Theframe 10 hears the luhher's line of the coiniass and is orovided withtruunions l2. 12 adapted to it in bear- 5 111 the gnnhal rings of thehinnacle, \Vl'ilt'.) have heeu ()l11iil'"(l from the diagram toi .iie -1of sin'iplieity.

The element. 9 is adapted to be driven b .J. i and adapted i .o engageone or the other oi two cortact; 15 mounted upon the ring 5to cause 1cservo motor to rotate in one direction or the other. For simplicity the.ircuit conne tie is between the device and the motor llitfi beenomitted.

The stabilized ring 7 is provided with a p:-.ir of dep nding hracliets16 disposed in the north-south plane and carrying at their tower ends 1:ring); 17. within which is mounti1 1 vertical. Connected member if)which at its 'd to an adjusting device ta .iliaed ring 7., whereby maybe adjusted rel- HUNT-dell on the 1 u'ning' clockwise as indicated bythe arrows pperrinp; at the ventilating apertures in 1. It Wlll also heassumed that the conring 7 is provic ed with re rotor 1 ot the maingyroscope is tact 1d occupies it-s neutral position with respect to thetwo cooperating contacts 15 so high side of the gyroscopic elementtoward the ea:-

In anordance with the principle of the yroscope the plane of rotation ofthe rotor will remain lined in space. As the earth urns from und r theritor due to its rotr ion, the high side of the rotor will rise.releirely to the surface of the earth carrying; he ease with it. Thiswill cause the penduo is mars oi the rotor and case to be shifted ironiits position of equilibrium. or: in otlu-r words, t ie center ofgravity, C. it. of the oscopic element may be regarded as having beendisplaced toward the east t rein its normal position. This displacementwill produce a torque about, the horizontal supporting axis 66which'will nose the rotor the incline flKlS and case to precess filJOllbl-i, thus displacing their plane it respect to the plane of the inclined5 Under the nd assuned here. the north side of the case will move upaiid the south side will move down so that the co tact 14 will beshiftee from its neutral n sition with respect to the contacts 15 igagement only with the contact lying the soot-in thereby energizing theserv 13 to rotate in a direction to turn the power driven element 9counterclockwise to carry tl e :os 4-4: and 88 tor aid the meridian. Asthe movable parts or the instrument it"?! toward the meridian theinclination of the e' yroscopic element will gradually increase as theearth continues to turn r from under itthus increasing the tore ah itthe axis G-6 The rotor an: c w i therefore process about the axis at anincreasing rate, and the conta will keep er the srvo motor 13 en t r 9in motion and S-8 will thus be carried past the i i dian and toward thewest. This westorl inoveinentwill continue until the contact is againassumes its neutral position with respect to the contacts 15 todie-energize th servo motor 13. This will not occur until precessionabout the axis has ceased due to the absence of torque about the axis6-6D This last named condition will obtain when the parts oi theinstrument have turned so far toward the rest that the gyroscopicelenent lies at s normal inclination 045: ia with respect to the surfaceof the earth due to the tact that in the new position it as at thebeginning of the cycle of operations described above.

During the movement of the parts from east to west there will berelative movenient of the use with respect to the rot :1 about the axis2 of the latter entirely apart from the rotation of the rotor within thecase. In other words, during meridian seeking oscillations the case 3will turn in the plane of the rotor about t ie ::;is common to it andthe rotor, while the rotor is spinning about this same axis. At the sameEllllQ that the case is turning about the re or axis 2 it is alsoprecessing abou" "ts trunnion axis 1 The resultant nio -/ein::;nt ot thecase due to the movement imparted to it h the servo motor and that dueto precession will l' e about a vertical axis passing through theinterse 'tion oi the axes 4 at and (5-6.

'tcr the gyroscopic element has 'eached i nent o'" the eaith toiard itwill depression of its high side rclatii suriace of the earth due to the1' plane of rotation of the rotor. pression of the high side of willresult shitting its center of gra C. G, toward the east from its normalposition, thus producing about the horiitontal axis 6 G a torque whichwill he in the opposice direction to that produced when the elementi'usat eastern lin ot' tion. This torque will care the rotor and case aboutthe direction as to elevate the n the case and depress tie south side to"he inclined ring As a rcsu preces h neu Josition with respect t intoenga 'enient only with the one toward the south, thus energizing the lto turn or dark n a cl ckwise direction thorobv the axes 4L--i and 8-8across the meridian tUYVe-Htl the e. the i is more from the west towardthe meridian the inclination of the gyroscopic element 'li respect tothe sun of the 0: th will continue to decrease sii co the earth is turniii-g toward the element. The torque about t axis due to the shittingthe center of gravity of the element will thus be increased as will althe precession of or and ces about the axis d e. inn nstrument willcross the meridian tron: to east with the cession about the axis 4 -4 inthe opposite direction. The resultant movement oi the case will be abouta vertical axis through the intersection of the axes l l and 6-0, but inthe opposite direction to that in which it turned during the east to ust oscillation.

It the gyroscopic element be unatlecled by any other external forces itsoscillations Will gradually diminish in amplitude due to friction, andit will ultimately reach a settling point with its axis l-l lying in theplane of the meridian and at an angle a u i: to the surface oi theearth. he angle represents the dillerenre llQtV-FOQH the inclination 0:when the rotor is at rest and the inclination for the particularlatitude of the compass When its rotor is spinning. This angle is suchthat the pendulousness of the element will maintain a torque about theaxis 65 to cause the ole ment to precess about the axis 41-4; an angularvelocity equal to the component of. the angular velocity of the earthabout an axis parallel to the axis 44, whereby the element follows themovement of the earth about its axis. In order that the element -mayfollow the movement of the craft over the earths surface, itsinclination Will be subject to a further variation, represented by a inaccordance with the east-West component of the speed of the craftas willmore clearly appear hereinafter.

If the course of the craft be ehang ged the resulting movement inazimuth of the outer shell or element 10 Will tend to carry along theinner shell or element 9 and the 'ings 7 and mounted thereon. As thering 5 moves it Will turn the case 8 about the inclined axis 2 of therotor and will itself be slightly tilted about the axis H from itsnormal position with respect to the plane oi the case due to the factthat the trunuions 6., 6 by which it is connected to the stabilized ring7 move in a horizontal plane while the :ase moves in an inclined plane.This change in the relative position oi? the case 3 and ring 5 Willcause a displacement of the contacts 14- and 15 from their neutralposition with respect to each other, in a direction to cause the servomotor 13 to be energized to turn the element 9 in the reverse directionto that in which. it tends to turn by the movement imparted to thesin-rounding element 10 by the change in course of the craft. Thisreverse movement 01 the element- 9 Will turn the ring 5 and case 3 untilthe contacts 14 and 15 are brought back to their neutral position withrespect to each other. The instrument Will operate in the mannerdescribed above whenever there is any yaw of the craft. The servo motorwill always maintain the compass card in its true position with respectto the points ot the compass, While the element- 10 ,ees

which bears the lubbers line will turn about the interior parts of theinstrument in accordance with the movement of the craft. It, for anyreason, the servo motor should fail to function, t 1e element 9, rings 7and 5, and case 3 will continue With the element 10 instead of beingbrought back to their normal position by the motor. The case Will simplyturn freely about the rotor axis 2 with corresponding changes ininclination of the ring 5 until the parts have i: en restored tooperative condition, but there will be no danger of the instrument being injured in any Way.

the imtruinent shown in the drawings the gyroscopic e ement is inclinedat substanliallv to the surface o'l the earth. The ax s l-% will bear,therefore, a. diilerout angular relation to the earths axis at dillerentlatitudes, being perpendicular thereto at about south latitude andparallel thereto at about 30 north latitude. When the axis 4% isperpendicular to the axis of the earth, the spinning axis 2 2 isparallel thereto, and the element- Will follow the movement of the earthwithout any precession about the axis l l, because the element is movingin its own plane of rotation. The maximum precession will occur when therotor axis is perpendicular to the earths axis, that is, at about 30north latitude.

The rate of precession about the axis ll will theretore vary accordingto latitude. Since this precession produced by a torque about the axis0G, the torque must vary with latitude in the same manner as theprecession varies, being 01 maximum magnitude when the axis is parallelto the axis of the earth, as at 30 north latitude, and of zero magnitudewhen the axis 4-l perpendicular thereto, as at 60 south latitude. Inorder that the required ti'u-que may be produced to cause the necessarypretession about the axis 4 4, the gyraumopic eicniei'it Wi l assumedili'erent angular positions about "he east-West axis G-6 to shill; itscenter of gravity in accordance with the torque which should be appliedabout this axis. lu other Words, the varying degrees torque are producedby variations in the angle an which represents the deviation of thegyroscopic element when the rotor is spiui'iing from the inclination awhich the element assumes when the rotor at rest, due to the position ofthe compass on the earths surface.

Since at 60 south latitude no precession about the axis l l will berequired t cause the element to follow the movement of the earth,because the element moves in its own plane of rotation, there will be notorque about the axis 06 except such as maybe due to the movement of thecraft, and the inclination of? the element Will be equal to 0. a (1being zero. At 80 north loo and but some of them be parts into the posilatitude a will have its greatest positive value, because at thislatitude the maxinium torque must be appliedabout the axis 6-6 toproduce he preces about the L L iiiLb seat A simple form or" compasssuch as has been described above will, however, require such a long timeto settle on the meriliai that it would be unsuited for use even on landunless means were provided ""or damping its oscillations. If, on th'other hand, the compass be used on ship be cra, as we bethe usual case,the impulses c ue to roll" of the ship and other causes cient cause aninstrument form (0 oscillate indefinitely so th nev settle upon themeridian.

the instrument may be used for navigational purposes.

One damuin arrangement 'L'h 121 be 1 i J employed is shown in A ms. andwhi h the parts of the compass z the same reference charact n1 tec.simplicity. A mass 21 is the case 3 by means of a bail or the likepivotally attached to the (use at points 22, 22 on an lying at an angle[3 to the xis 4 ot' the case. The equilibrium pos .ion of the gyr opicelement, including the mass 21, when it occupies its normal inclinationo;

l or'the sake of -uspended from surface of the earth shown ll inAssuming, as in the first description of the operation or" the t that itstarts from an east position, the r 1; clination of the element will beincreased from an ie (l ofi olg bv an an 'le a. as the :3 H c p earthturns rroin n der it, thus slnrting the tron shown in broken lines l, itbeing understood that in these simple figures of tie apparatus and inthe accompanying diagrams relative d3 ments between parts of theinstrument under different condition" are greatly exaggerated forclearness or" disclosure.

As the tilt of the gyroscopic element about the axis 6-6 increases themass 21 will be shifted from its normal equilibrium beneath the case;The effect upon the ele- Leta L) rep- 1 t about o- 1n -reases L i u.-oq,--o.s r0, e resolved into two u an axis perpenot the mass 21,

. the axis 22-22. uspe 'l i'reely from the case the last named com) wentdoes not r movemeiu; t 1e -n1ass but t t (z c rcprc: a mov aunt "s wi hth ase due to the hiring;

'th-west bearing of tl e bail and 251 of its north-cast bearing.

uh ponent may be rcsolvcd into two components a (Z and (Z. c, as shownin 6. The component (Z c represerts movement of the mas 21 about thesupporting axis 6-43, but this will merely add to the pendulousness ofthe gyroscopic element and Increase its nieri lian seeking properties.The component (7 represents the movement of the as 4- 1 about lie supperine e v t this movement 1 i I 1, w 1 z oe LO apply a tOiqll -J scoutthis a Wlll cause p ecession about the h .i ,e o u e gyro- I emcnt andelevating the lower side. t is therefore i :ts in the unistrument shownin FIQ'S.

reoue tr below that which e of i p 'oachc-s its nor-ma value and nintermediate between w I x thus r: dui

ng subsequcit oscillations 1 the plai= e oi the meridian normalinclinationw The character tic curves of the two forms of compass areshown in 7 in which the path traced out by the k of the undampedinstrument of 1 and 2 viewed from the north is represented by theellipse A plotted with respect to coordinate axes in whiclthe ordinatesrep) inclination and the abscissze displacement in azimuth. The majoraxis 6 of the ellipse corresponds to the normal inclination d ar ag ofthe sensitive element, while, the minor axis g 7:. corresponds to themeridian.

The curve B repress its the path t'aced out by the axis el l of thedamped instrument of 3., showing the manner in which the inclination anddisplacement of about its axis 8-S since the contacts 15 need Wheneverthere is a component of precession about the axis 44 there will be acorresponding movement of the contact 14 wit respectto the contacts 15,but the component about the axis 6 6 will not affect the relativeposition of the contacts. In order that there may be no displacementbetween the contacts, Which would energize the servo motor 13 to turnthe element 9 from its true position with respect to the points of thecompass and thus produce an error in the indications of the instrument,the contacts 15 may be shifted by an amount equal to that by which thecontact 14 is shifted due to the component of'precession about the axis4-4.

The contacts 15 may be shifted most conveniently by tilting thestabilized ring 7 about its supporting axis 8-8 to tilt the ring 5, onwhich the contacts are mounted, about the axis 44. In the simple form ofinstrument shown in Figs. 1 and 2 this tilting may be effected by meansof the adjusting device 20 connected to the ring 17 which is maintainedin a fixed plane by the stabilizing gyroscope 18 mounted therein. Achange in the length of the member 19 by manipulation of the device 20will result therefore in a tilting of the ring 7 about its axis 8-8,thus shifting the contacts in one direction or the other from theirnormal position in accordance with the amount by which thecontact 14would be shifted due to the component of precession about the axis 4-4,this component depending upon the course and speed of the craft.

VVhen the craft is moving east or west there is no component ofprecession about the axis 44, so that'under these conditions thestabilized ring 7 should not be tilted operation a manual adjustment hasbeen shown in the simplified diagrams.

If the speed of the craft be changed, while maintaining the same course.the torque pro- I duced by the pendulousness of the element about anaxis lying in a plane perpendicular to the plane of tne greatcirclealong which about the axis 44, the component willvary .also, andthus alter. the nioi' ementof the contact 14 with respect tothefcontacts 15.

,ln orderto prevent the servo notor 13 ceased.

being energized the stabilized ring 7 may be shifted by means of theadjusting device 20 to bring the contacts 15 into a new neutral positionwi h respect to the contact 14, this new position being thatcorresponding to the new speed of the craft, so that there will be nodeviation of the compass at this speed.

So far the component of precession about the axis 66 is concerned itwill morely shift the center of gravity of the element in the verticalplane of the axis 44 without affecting the position of the contact 14with respect to the contacts 15 so that no correction need be appliedfor this compo nent.

In the manner described above the gyroscopic element will continue tofollow the movement of the craft over the surface of the ear h at thenew speed, and there will be no deviation of the compass as a result ofthe acceleration or retardation of the craft. In other words, thearrangement of the parts of the instrument is such that under conditionsof change of speed the gyrosc pic element will follow the motion of thecraft over the surface of the earth, and by suitable, shifting of thecontacts 15 for each new speed all ballistic deflections due to suchchanges are avoided.

It has been explained above that the gyroscopic element is caused tofollow the movement of the craft over the surface of the earth andmaintain its normal inclination thereto by the shifting of the centervof gravity of the element as a' result of the precession caused bythe-torque about an axis lying in a plane perpendicular to the plane ofthe great circle along which the craft is travelling.

lVere the servo motor energized by the shifting of the contact 14 due tothe component of precession about the axis 4-4, the case would be turnedabout the rotor axis 2 until this contact had been restored to normalposition with respect to contacts 15, that is, until precession aboutthe axis 44 had The center of gravity of the case would then occupy itsnormal position below and in the vertical plane of the axis The effectof the pendulousness of the ele-- merit in producing a component torqueabout the axis H would therefore be overcome, and there would be nocomponent about the axis 66 of the precession which causes thegyroscopic element to follow the movement of the craft over the earthssurface. The deviation of the element from its normal inclination wouldthen be increased as the craft moves, and the resulting torque due tothe pendulousness of the elementwould again cause precession about anaxisat right angles to that about which the torque is applied. Thecomponent about the axis 44 ofthis precession would shift the contact 14to again energize the servo motor to 'turirthe inner frame 9 and theparts mounted thereon until the contacts were restored to their normalrelation.

The eiiect of the actions describedv above would be to produce stillfurther error in the indications of the instrument unless this eficctwere compensated for. Such compensation may be obtained by suitablytilting the stabilized ring 7 to shift the contacts 15, in the mannerpreviously cescribed, to prevent the servo motor from being energizedand annulling the effect of the pendulousness oi the gyroscopic elementin causing it to follow the movement of the craft over the surface ofthe earth.

It has been explained that the simple form of instrument shown iii-Figs.1 and 2 automatically takes care of changes in latitude; but when thedamping arrangement shown in'Figs. 3 and 4 is employed a latitudecorrection is required for the following reason. Changes in inclinationof the gyroscope element due to changes in latitude of the craft uponwhich the compass is carried will be accompanied by correspondingchanges in the position of the mass 21. Since this mass is mounted toswing about an axis lying at an angle to the north-south axis 4-4 of thegyroscopic element, such changes in inclination of the element wouldcause the mass to 'be'displaced slightly to one side or the other of thevertical plane of the axis l{l, thus producing 'a torque about thisaxis. Theelemcntwould thus be caused to process about theiaxi's' 66,thereby producing further changes in the inclination of the element andaltering the precession about the axis 4el so that it would notcorrespond exactly to that which should take place at the particularlatitude. These effects, although slight, would produce a change in theposition of the gyroscopic element as compared with the position whichit should normally occupy at the particular latitude, with the resultthat the compass would have a settling point displaced slightly from itstrue position with respect to the meridian, and an error would beintroduced in its readings. v

In order to correct for the effect of the displacement of the mass 21due to changes in latitude the stabilized ring 7 may be shifted to raiseone or the other 01 the truninions 6, 6 to displace the center oi?gravity of the case from its normal position below the 'ELXIS 44 to theeast or west enough to pro- 18, but insulated therefrom in any suita theinvention is'shown in'l igs. 8 to 14 inclusive and 17, in which theelements of the I bearings in the outer shell 10, instead (if beingattached to the shell and adapted to ex tend into bearings in a gimbalring as shown in the simplified diagram of Fig. 1. The innergimbal ring23 is provided with trunnions 241-, 24: disposed at right angles to thetrunnions 12, 12 and extending into suitable hearings in an outer gimbalring 2 5 which is supported; as by means of sp'ringsQIG' from the upperedge of the 'binnacle bowl 27. The binnacle is provic'led with asuitable transparent cover through which the compass card- 28 carried onthe inner shell 9 and the lubbers line 29 on the outer shell 10 may beseen. 7

In the simple form of'instrument shown in Figs. 1 to 4: the case 3 isshown support-ed upon the ring 5 by the simple trunnions 1, 4; but inthe complete instrument these trunnions areutilized for conducting thecurrent to the stator of the main gyroscope 1. and therefore are notofthe simple construction shown in the diagrammatic figures. Thesamegeneral construction of trunnicns may be used for conveying the currentbetween the stabilized ring 7 and the inclined ring 5 and also betweenthe ring 17 and the stabilizing gyroscope 18 mounted thereon. Inordernot to complicate the drawing only one set of such conductingtrunnions has been shown, and for convenience the trunnions of thestabilizing gyroscope have been selected for this purpose. It will beunderstood that the other trunnions through Wll ich the circuits passare of substantially the same construction except as may be notedhereinafter.

It-is intended that both of the gyroz-sciip'es of the instrument shallbe operated by three phase current and accordingly one of thetrunnions,- such as 30 (see Fig. 10), is uitilized for two of theconductors of a three phase system/while the other trunnion 31 isutilized for the third conductor of the systenrand is grounded asindicated in the wiring diagram Fig. 1d. The trunnions may be of anysuitable construction adapted to serve this purpose. Byway oi'illustration the trunnion 30'is shown herein consisting of a member 32mounted wr in an aperture in the ring 17 and insulated there rom by acollar 33 of suitable material. Screwed within the member 32 is atrunnion 34' which extends into a ball bearing placed in a recess in thecase of thegyroscope manner as by being mounted within an annular member36 of insulating 'inaterial. The trunnion 34% is provided with alongitudinal bore lined with insulating material 37 and containing a pin88, the inner end of which is held in engagement with a plate 39 setwithin the insulated member 36 of the bearing, by means of a springfinger &0 attached to, but insulated from, the ring 17.

It is intended that one of the conductors of the three phase systemshall be connected to the spring 40 so that the current will passthrough this spring and the pin 38 to the plate 39 from which av leadmay be carried in any convenient manner to one set of coils of thestator of the gyroscope. Another one of the conductors of the threephase system is electri tally connected in any suitable manner to themember 32 so that the current passes from this member through trunnion3% and the balls of the bearing 35 to the raceway of the balls fromwhich a lead may carry the current to another set of coils of thestator.

The grounded bearing 31 consists trunnion 41' screw threaded in the ring17 to permit adjustment. The inner end of the trunnion extends into asuitable ball bearing 42 mounted within a recess in the case of thegyroscope. The third set of coils of the stator of the gyroscope isconnected to the raceway or" the ball bearing 42 so that current maypass through the balls of the trunnion 41 tothe ring 17 which isgrounded with the other parts of the instrument.

The upper bearing 4 of the case 8 of the main gyroscope IS 01"substantially the same construction as is the trunnion 30 of thestabilizing gyroscope, and the parts WlllCh appear in Figs. 8 and 9 havebeen designated by the same reference characters as used in connectionwith the description oi? the trunnion The upper trunnion 4 differs inone respect from the construction shown in Fig. 10 ,in that he trunnionmember 34 is mounted eccentrically. within the 7 member 82 in order thata fine adjustment of the upper end of the trunnion axis 4:4 of the casemay be obtained by turning the member 32 within the aperture 1n which itis} mounted in the ring 5, as shown most clearly in Fig. 17.

The lower end of the axis a d of the case is formed by a trunnion ofsulstantia ly the same construction as the trunnion 81 of I 10, butwhich in addition performs the function of a thrust hearing on accountof the inclined position of themain gyroscope.

The gyroscopic rotor and case and the ring 5 arepivotally mounted by thetrunnions 66 between upstanding lugs or ears projecting from the top ofthe stabilized ing as shownniost clearly injFig'. 9. 7 To provide forthe conduction of current be Figs. 10 and 11.

tween the ring 7 and the ring 5, one oi the trunnions (l, the easttrunnion as shown an ill the same manner is the trunnion 3 0 of Fig. 10.The parts which in Fig. 10 are shown mounted upon the ring 17, are, inthe trunnion 6, mounted upon the ring 5, while the insulating member 36and the ball l earing therein are mounted upon the ring 7. In order toprovide a ground connection between the ring 5 and the ring 7 there isattached the former a bracket i l passing over the top of the ear 43 andprovided at its free end with a contact point 45 lying in line with thetrunnion axis 66. Cooperating with the contact point 45 is a bracket reattached to the outer face of the stabilized ring 7 at a point below thetrunnion. The brackets lel and i6 are of spring material so as tomaintain a good electrical connection between them. a

Flexible leads or pigtails may be connected to the terminals of the easttrunnion 6, that are associated with the stabilized ring since this ringwill not be affected by the resiliency oi such leads. The other ends ofthe leads are connected to rings 4-7 and of a series oi slip rings 47 to50 inclusive which surround the inner frame or shell 9 and are attachedto the lower side of an outwardly projecting ledge or shoulder 51 at thetop of this shell by means or" screws passing through insulating spaces52, (see Fig. 9). These slip rings are to take care or". the relativemovement between the inner shell 9 to which they are at ached and theouter shell 10 which partakes of the movement of the craft. For thepurpose o1": conducting current to the slip rings there is provided foreach ring a brush 53, all of the brushes being attached to an insulatingbase 54 which is mounted in a suitable aputurc in the outershell 10 asshown most clearly in The spring fingers are provided with, bindingposts 55 from which leads maybe carried to the external circuit.

The trunnions 8, 8 of the stabilized ring 7 are screw threaded throughthe ring to provide for adjustment and extend into suitable ball.bearings 56 in the inner shell 9 as shown most clearly in Fig. 9. Thebrackets 16, 16 depending from the stabilized ring are arranged in thenorth south plane and may be of any convenient form. They are providedat their lower ends with trunnions 57 for supporting the ring 17 of thestabilizing gyroscope 18, the hearings of which have previously beendescribed in connection with Fig. 10.

The servo motor 13 for turning the inner shell 9 and the'parts mountedthereon may be of any suitable construction and is shown only in anexternal view in Figs. 10 and 12. Forthe purpose of supporting the motorand the gear connections between and the inner shell there is provided aframe consisting of lower and upper plates 58 and 59 respectively,connected by blocks 60 which are attached to the inner face of the out-rshell 10 by screws 61. The servo motor is carried by the lower plate 58and its shaft 62 is provided with a pinion 63 meshing with a. gear 6 Lat'ached to a shaft 65 mounted between the plates 58 and 59. The shaft65 is provided with a pinion 66 meshing with a gear 67 on the upperendof ashaft- 68 mounted between the plates 56 and 59. Also mounted uponthe shaft 68 is av pinion 69 which engages a gear 76 attached to thebottom of the inner shell as shown most clearly in Fig. 9.

The. transmitter for controlling the actuation of 'egeatcr compo es mayconveniently be operated from the gear train of the servo incurs. will.be understood that any suitable form of transmitter may be used for thispurpose. A

as shown herein a contact device 11. is attached to the lower face ofthe gear 64; and is provided with segmentalprojecting port is 72 shownmost clearly in Fig. 16 adapted to engage brushes 73 as the member 'Zlrotates. The brushes are mounted upon a plate 74 (Fig. 12) of insulatingmaterial. attached to the bottom of the plate 58, and are provided withconductors 75 leading to the repeater compasses.

The contact mechanism for controlling the servo motor and which has beendesignated by reference numerals i l and 15 in the simplified diagrams,may be of any suit-- able construction. shown herein the part 141- ofthe mechanism is in the form of a trolley cooperating with the parts 15.A bracket 76 of resilient material is fastened to the upper face of thecase 3 (see Fig. 9) and carries at its top a member 77 to one side ofwhich is attached an upwardly e2:- tci ling linaclret 78 carrying at itsupper end j wheel 79 adapted to roll over the cooperating parts 15 ofthe mechanism, whichare mounted upon the inclined ring 5 by means of aresilient bracket 80. The portions l5 of the mechanism are constructedsuitable material to cooperate with the or trolley wheel with a minimumai'nount of injury due to arcing, but those portions may be c temledsidewise to serve as hearing sur- :es for the trolley wheel in case thelatter houhil be shifted beyond the parts particularly designed tocoinierate therewith. The parts 15 are separated slightly from eachother as indicated at 81 and each of them is provided with a terminal towhich a suitable lead may be connected.

in order to con'iplete the circuit between the contac and a relativelyfixed part of the instrument, which does not partake of theLiC'VQlAGl'lt of ring 5, the west trunnion 6 of this ring may beutilized in a manner similar to that in which the east trunnion utilizedforthe circuit of. the gyroscope.

For this purpose the west trunnion 6 is of substantially the sameconstruction as the trunnion of the stabilizing gyroscope described in.connection with Fig. 10. There is, however, a difference in structuredue to the fact that the reaction of the spring 40 associated with theeast trunnion 6 tends to press the ring 5 toward the west, and thereforein the west trunnion 6 the spring it) is on'iitted and the pin 38 isfixed with respect to the trunnion member 8% so as to be held inengagen'ient with its cooperating conducting plate 39 by the effect thespring 40 on the other side of the instrument. T he leads from theterminals 82 of the contact mechanism may he carried along the ring 5and connected to the two current conducting parts of the west trunnion6, associated with the ring. From the parts of this same trunnionassociated with. the stabilized ring Z flexible conductors or pigtailsare carried to the intermediate slip rings t8 and 49, and through thebrushes 53 coacting with these u e the circuit may be continued to thevo motor 13 by suitable leads.

. shown most clearly in Figs. 8 and 9 the care 2'} is provided with apair of brackets 83 between the outer ends of which is a screw 84kcarrying a weight 85, the arrangement of parts being such that theweight is movable in a direction perpendicular to the axis 4- l for thepurpose of accurately balancing the gyroscope about this axis.

For the purpose of applying the necessary ried, there isprovided a ring86 which, as shown. most clearly 1n Fig. 10', is mounted between fourbrackets 87 attached to the inner face of the outer shell lO'atsubstantially 90 apart. Each of the brackets is provided with a roller88 which engages the periphery of the ring 86. At diametrically oppositepoints the ring 86 is cut away to provide depressed cam faces 89 whichare arranged to cooperate with the rollers 88 of the. north and southbrackets 87, the arrangcment being such that when the innermost part ofone cam engages its cooperating roller the outermost part of the othercam is in. engagement with its roller as shown most clearly in Fig. 10.

The cam ring 86 is adapted to be moved circumferent-ially in accordancewith the speed of the craft and for this purpose an.

The'arm may be provided with a knob 94: for convenience in manipulatingit. Since under norniai con raduated in units- I are ca terminals of theconducting trunnion 6 at the east side of the instrument. From the otherditions the speed of the craft will not be changed frequently thecorrection for this quantity may be applied manually, although it willbe understood that if desired the arm- 90 can be connected to a suitablemechanism whereby it may be swung automatically in which extends aplunger 97 having its outer end in engagement with the arm 95 and itsinner end in engagement with the outer end 023 one arm of a bell cranklever 98 pivotally mounted betweenthe two parts of the cor- -espondingbracket 16 which is provided with suitable lugs to receive the pivot 99of the lever. Theother arm of the lever engages the free end of an arm100 which, as shown most clearly in Fig. 13, is attached to the lowerend of a rod 101 mounted in a guide 102on the stabilized rin 7 andprovided at its upper end wit-h an adjusting nut 103 graduated in unitsof latitude and cooperating with a fixed member 104 which bears an 7index mark as shown most clearly in Fig. 10.

Attached to an intermediate point of the arm 100 is a link 105, theother end of which is connected to the top of the ring 17 with in whichthe stabilizing gyroscope 18 is mounted. On the opposite side ofthesupporting bracket 16 is a spring 106 connected between the bracket andthe ring 17. The arrangement is such that the spring 106 tends to turnthe ring 17 about its trunnions 57 and through the link 105 hold thefree end of the arm 100 in engagement with the end of the horizontalarmof the bell crank lever t 8 and through the latter push the pin 97against the arm 95 to hold the roller 96 firmly in contact with theinner edge of the cam ring 86, thus preventing any lost motion betweenthe elements of the correcting mechanism.

A diagram of the complete circuit connections of the instrument is shownin Fig. 14 in which 107, 108 and 109 represent the mains of a threephase system, the main 109 being grounded] Current is-supplied from thenongrounded mains 107 and 108 to the slip rings'47 and 50 through thebrushes 53 and 53 which are connected to the mains by leads 110 and 111respectively. Connected to the slip rings 47 and 50 are-conductors 1 12and 113 respectively, which are carried to the stabilized ring 7,preferably in the neighborhood otfone of its trunnions 8, and thenbranched into a pair of conductors 114 which ed along the stabilizedring to the terminals of the part of this trunnion associated with theinclined ring a pair of leads 115 is carried along the ring to theterminals of the conducting trunnion 4 at the north side of the case 3.The terminals of the trunnion bearing which is carried upon the case areconnected by leads 116 and 117 to two of the terminals of the threephase windings 118 of the stator of the main gyroscope. The thirdterminal of the windings is grounded through the trunnion 4 at the southside of the case, the ring 5, springs 44 and 46, the ring 7 and theouter parts of the instrument.

F or the purpose of supplying current to the stabilizing gyroscope 18 abranch pair of leads 119 is connected to the leads 112 and 113 andcarried along one of the brackets 16 and around the ring 17 to theconducting trunnion of the stabilizing, gyroscope where they areconnected to the spring and the member 32. The ball bearing 35 and theplate 39 of this trunnion are connected by leads 120 to two of theterminals of the three phase windings 121 of the stator of thestabilizing gyroscope, the third terminal being grounded through theconoucting trunnion 31 at the. opposite side of the case.

he servo motor 13 may be of any suitable reversible type. As shownherein it is a three phase motor having two of its terminals connectedto the mains 107'and 108 by conductors 122 and 123 respectively. Theother terminals of the motor are connected by conductors 124 and 125 tobrushes 53 and 53" which bear against the slip rings 48 and 49. A pairof leads 126 is connected to outer terminals of the conducting. trunnion6 at the west side of the instrument. The terminals of this trunnionwhich are associated with the ring 5 are connected by means of leads 127carried along this ring to the terminals 82 of the contacts 15. Thecooperating contact 14 is grounded through the case of the maingyroscope as previously explained. For the purpose of preventingsparking at the contacts the slip'rings 48 and 49. are connected througha resistance128 the midpoint of which is grounded.

In the operation of the complete apparatus described above the currentis supplied to the stators of the main and stabilizing gyroscopes overthe circuits and through the conducting trunnions as shown in thedrawings and described above. that the rotor 1 of the main gyroscopeshall process in a direction to cause the instrument to operate in theproper manner. it must spin clockwise, as indicated by the 221TO\ inFig. 8. when the center of gravity of the gyroscope is below itssupporting In order axis 6-6. If it be above this axis the rotor mustspin counterclockw1se. The rotor ot the stabilizing gyroscope 18 mayspin in either direction since its only purpose is to.

stabilize the ring 7 about its north-south axis 88 to maintain theeast-west axis 6-6 in fixed relation to the surface of the earthtoprevent the contacts 15 on the inclined ring 5 from being displaced dueto rolling and pitching oi the craft upon which the con'ipass iscarried.

Whenever the gyroscopic element is dis placed from its normal positionwith respect to the points of the compass, the torque produced by thependulousness of the element about its axis 66 as the earth turns awayfrom or toward the iixed plane of rotation oi the rotor. will cause therotor to precess about an axis perpendicular to the axis 6-6,

thus shifting the trolley 79 from its normal position between the twocontacts 15 on to one of these contacts to energize the servo motor 13over the circuits described in connection with Fig. 14. The servo motorwill drive the azimuth gear through the gear train consisting of pinion63 on the shaft of the motor, gear 64;, pinion 6G, gear 67, and pinion69 meshing with the azimuth gear 70. Were it not for the backlash in thegears and the inertia of the moving parts of the servo motor the trolley79 would remain upon the contact 15 upon which it was shifted by theprecession of the rotor, to permit the servo motor to bedrivencontinously in one di rection. Owin however, to these factors thetrolley 79 will usually oscillate between the two contacts 15, even whenthe gyroscopic' element is not seeking the meridian. The effect of themeridian-seeking. precession oi the rotor will, when combined with theoscillatory movement of the trolley 79, result in the trolley remainingfor a longer period upon one ot'the contacts 15 than upon the other sothat the servo motor will cause a progressive movement of the shell 9and the parts mounted thereon including the stabilized ring 7, theinclined ring 5 and the The PI'GCGSSlODtl' motion or the case rotor 1while seeking the meridian will result in a gradual shifting toward the1i1eridia'n of its high point, and the servo motor will turn the caseabout the rotor axis 22 to keep the upper trunnion 4 at the high pointof the rotor. This action will take place whenever there is anyprecession of element, the trolley 79 will act in connection w th thecontacts 15 to reverse the direction of rotation of the servo motor tocause the shell 9 and parts mounted thereonto turn corresponding to thelatitude at which the the instrument is located and the speed and Vheading of the craft.

The mass 21 for damping the oscillations of the gyroscopic element isshown in Figs. 8 and 9 in the form of an annular member surrounding thelower hub of the case with sufiicient clearance to allow for therelative movement between the mass and the case during the oscillationsof the element. The annular member 21 functions in precisely the samemanner as does the mass 21 shown in Figs. 3 and l and described above.

Whenever the course of the craft is changed the movement in azimuth ofthe shell 10 which bears a fixed relation to the craft, will tend tocarry along the inner shell 9 and the parts mounted thereon includingthe stabilized ring 7 the inclined ring 5, and the case. There will thenbe a change in the relative position of the ring 5 and the case 25 dueto the fact that the trunnions G, 6 of the ring move in a horizontalplane on account of their connection to the stabilized. ring 7 while thecase turns about the inclined axis 2-2 common to it and the rotor. Thisrelative movement between the case 3 and the ring 5 will result in adisplacement of the trolley 7 9 on to one of the contacts 15 to energizethe servo motor 13 to turn the shell 9 in a direction opposite to thatin which it tends to turn by the movement of the outer shell. 10. Thecase will thus be brought back to its normal. position with respect tothe rotor and the trolley understood that in the actual operation of.

the instrument the displacement of its parts and the time required forthe operations described above will be of small magnitude, so that inpractice the inner shel 9 and the parts mounted thereon, including thecom pass card 28, will be maintained in their true posit-ion withrespect to the gyroscopic element and hence with respect to the pointsof the compass, while the outer shell 10 carrying the lubbers line 29will turn with the craft so that the angle between this line and thenorth or zero point of the compass card will indicate at all times theheading of the craft. It will also be understood that the plate 74 ofthe transmitter partakes of the motion of the servo motor to control thecircuits of repeater compasses and produce a movement of their compasscards corre-

